The field encompassing ground movement of aircraft is well-known in the prior art. In the industry, the engines of the aircraft are almost exclusively used to move the aircraft around an airport, typically when taxiing to or from a runway. These engines are generally speaking very loud and, when operating for the purpose of ground movement, they burn large quantities of fuel. Safety reports posted on a NASA government website have remarked on several incidents where people have been knocked off a lowered stairway of a second aircraft by the jet blast from a nearby first aircraft taxiing to or from a runway. The same report, Aviation Safety Reporting, System (ASRS) Directilne, Issue Number 6 for August, 1993--available at http://olias.arc.nasa.gov/asr/d16_blast.htm--also discusses damage to other aircraft due to the ground jet blast hazard of nearby taxiing aircraft. These jet engines may cause violent air disturbances in the near vicinity of the aircraft, and also contribute to noise and air pollution.
In addition, the costs associated with the period of time an aircraft idles on the taxiway, as well the length of time for taxiing to a runway, are very large. The chart below details a cost summary for certain major airlines, on the basis of a total idling time of 20 minutes or 1 hour per day per aircraft per airline, using typical fuel consumption figures and an average cost of fuel per gallon. The "idle" time being considered is that time spent by the aircraft from the moment the engines are started until the aircraft reaches the end of the runway for takeoff, minus a typical warmup time of three minutes per engine. The idling time therefore includes all time after pushback, such as taxiing time, and standing in a queue of waiting aircraft on a taxiway. It is believed that such idling time is not less than 20 minutes per aircraft per day, and may be much more.
Cost for 1 Year to: Airline Cost for 1 Year to: Idle 20 (37.5% of Fleet) Idle 1 hr./ Day Min./Day Canadian Airline No. 1 $14,842,915 $4,947,638 US Airline No. 1 $26,699,809 $9,899,936 British Airline No. 1 $26,965,859 $8,988,620 US Airline No. 2 $16,638,040 $5,546,013 US Airline No. 3 $33,596,174 $11,198,725 Courier No. 1 $20,515,312 $6,838,437 US Airline No. 4 $26,892,175 $8,964,058 US Airline No. 5 $42,785,894 $14,261,965 US Airline No. 6 $17,233,063 $5,744,354 Assume: Fuel Consumption: 3200 lbs/hr/aircraft 6 lbs/US gallon Fuel Cost: $0.95/US gallon
The above chart outlines the saving that could be obtained by the airlines by either eliminating or reducing the idle rime of the aircraft in their fleet. This leads to the field of ground movement of aircraft as it relates to the use of an external vehicle to facilitate that around movement. Tractors, dollies, or tugs, as they are sometimes called, exist in the present day in a number of different embodiments. Typically, the operator manned vehicles provide a means of coupling the vehicle to the aircraft at which point the aircraft is pushed or towed. The means for coupling is commonly a tow bar system which cradles the nosewheel of the aircraft and further provides an attachment point to the aircraft such that, when in place, the aircraft may be to the pushed or towed. In the alternative, a dolly may also be designed to receive the wheels of an aircraft and, when the wheels are in place on the dolly, the aircraft again may be pushed or towed. The means for coupling may be manual or operator controlled. The most typical use for aircraft tractor vehicles is for pushback from the terminal gate after the aircraft is loaded for its next flight; and sometimes for towing an aircraft to a hangar for maintenance operations.